Press-forming machine

ABSTRACT

A press forming machine comprising driving shafts for pressing three or more respective pressure points and displacement measuring means for measuring a displacement close to the pressure point. A central driving shaft among the driving shafts has a gap (the slack) larger than those of other driving shafts between each of the driving shafts and a pressure plate. During press formation at a trial stage, a positional displacement close to each pressure point is measured by the displacement measuring means and control data is supplied to each driving source for driving a driving shaft to drive the pressure plate. Then, production press-formation is performed in accordance with the above result. Therefore, the central driving source can avoid overload by the slack of the driving shaft with the pressure plate.

TECHNICAL FIELD

The present invention relates to a press forming machine used to form ametallic plate, particularly to a press forming machine capable ofkeeping a pressure plate for setting a movable mold at a desiredposition of a fixed mold.

BACKGROUND ART

A press forming machine is also used for punching press, drawing, stampforging, and injection molding. A press forming machine is generallyused in which one mold is fixed and the other mold is movable. Avertical press forming machine includes a lower fixed plate, a pluralityof supports supported by the lower fixed plate, an upper support plateheld by the supports and a pressure plate capable of reciprocating alongthe supports between the lower fixed plate and the upper support plateand having a forming space between the pressure plate and the lowerfixed plate. A fixed mold is mounted on the lower fixed plate and amovable mold is set to the downside of the pressure plate in the formingspace and a workpiece is formed between the fixed mold and the movablemold. The pressure plate is normally planar and vertically moved by adriving mechanism. It is preferable to press-form, while keeping themovable mold at a desired positional relationship with the fixed mold,for example, to press-form by moving the movable mold while keeping ithorizontal. Therefore, the pressure plate is moved while being kepthorizontally. The support is built so as to be thick and have a rigidityin order to prevent the pressure plate from tilting during thepress-formation. However, the pressure plate or the like is bent and atilt occurs due to the clearance of a slide portion in some cases.Therefore, it is necessary to correct a mold in order to prevent thetilt.

Moreover, because a workpiece formed through press forming has a complexshape such as a three-dimensional shape, it is found that not only themagnification of a force applied to the pressure plate is changed inaccordance with progress of press-formation but also the position towhich the force is applied moves in accordance with the press-formation.

When a vertical resultant force of forces working on the pressure plateis applied to the central position of the pressure plate, an angularmoment for tilting the pressure plate is not created to the pressureplate. But, since the position at which the force works is moved asdescribed above, the position and the magnitude of the angular momentare changed. Therefore, deformations of various portions of a pressforming machine such as an elongation and a warp of the pressure plate,the upper support plate and the fixed plate which occur during thepress-formation are changed in accordance with progress of thepress-forming.

Because a descending progress of the pressure plate is changed due to aload applied to the pressure plate or deformation of the press formingmachine due to the load, the positional relationship between the fixedmold and the movable mold or the pressure plate may not be horizontal.Therefore, the present inventors improved a press forming machine havinga plurality of driving sources for driving a pressure plate and proposeda press forming machine capable of keeping a pressure plate horizontalby controlling the driving sources in Japanese Patent Laid-Open No.2002-263900. In the proposed press forming machine, a pressure plate iskept horizontal by supplying a driving pulse signal having a frequencyhigher than a predetermined frequency to a driving source (servomotor)set to a position close to a portion whose progress is delayed on thepressure plate and supplying a driving pulse signal having a frequencylower than the predetermined frequency to a driving source whoseprogress is relatively advanced. However, it is found that when anoverload occurs in a driving source present at the central portion ofthe pressure plate, a phenomenon in which the above adjustment cannot bemade occurs.

In the above proposed press forming machine, when having three or morepressure points on the pressure plate among which a pressure pointpresent at the central portion is surrounded by the pressure pointspresent on the periphery, a driving source for driving a driving shaftset to the pressure point at the central portion may be overloaded. Whenforming a workpiece by holding a forming mold between the pressure plateand a fixed plate, a load larger than the load at peripheral portion isapplied to the central portion of the pressure plate. Therefore, thedisplacement of the central portion is most delayed. Therefore, moredriving pulse signals are supplied to the driving source for driving thecentral driving shaft, and displacements of the central portion andperipheral portion of the pressure plate are equalized to keep theirhorizontal state. However, the driving shaft set in the center of thepressure plate is applied to by a load larger than that applied to eachof a plurality of driving shafts present at the peripheral portion,since part of a load applied to each of the driving shafts on theperiphery works on the central driving shaft and a total load is appliedto the central driving shaft. Therefore, it is estimated that thedriving source for driving the central driving shaft is overloaded.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide a pressforming machine capable of avoiding the overload of a driving source setto a pressure point between a plurality of pressure points or a pressurepoint surrounded by a plurality of pressure points and individually orseparately driving each of the driving sources so as to keep a movablemold at a desired positional relationship with a fixed mold when pressforming is progressed.

A press forming machine according to the present invention comprises:

a fixed plate;

a pressure plate facing the fixed plate, having a forming space betweenthe pressure plate and the fixed plate and being capable ofreciprocating;

a plurality of driving shafts for pressing the pressure plate at threeor more respective pressure points distributed on the pressure plate byengaging with the pressure plate;

a plurality of driving sources for respectively driving the plurality ofdriving shafts;

control means for independently driving and controlling each of theplurality of driving sources; and

displacement measuring means for measuring a positional displacement ofthe pressure plate adjacent each of the pressure points,

wherein at least one pressure point (hereinafter referred to as “centralpressure point”) among the pressure points is set between or surroundedby other pressure points (hereinafter referred to as “peripheralpressure points”),

a gap between a driving shaft engaged with the pressure plate at thecentral pressure point and the pressure plate is larger than a gapbetween a driving shaft engaged with each of the peripheral pressurepoints and the pressure plate, and

the control means is provided with means which measures the positionaldisplacement adjacent each of the pressure points by the displacementmeasuring means on each of a plurality of operation stages during apress-forming operation, detects a state in which the entire pressureplate is kept at desired displacement positions, extracts a control datafor each of the plurality of driving sources to keep the entire pressureplate at the desired displacement positions, supplies the extractedcontrol data to each of the plurality of driving sources, andindividually drives the plurality of driving sources.

In the press forming machine above, it is preferable that the drivingshaft engaged with the pressure plate at the central pressure point hasthe gap of 0.01 to 0.2 mm between the driving shaft and the pressureplate.

In the press forming machine above, the control means may be providedwith means which measures a positional displacement adjacent each of theperipheral pressure points by the displacement measuring means on eachof the plurality of operation stages during the press-forming operation,detects a state in which the vicinities of the peripheral pressurepoints are kept at a desired displacement position, extracts a controldata for each of the plurality of driving sources corresponding to theperipheral pressure points to keep the vicinities of the peripheralpressure points at the desired displacement position, supplies theextracted control data to each of the plurality of driving sources, andindividually drives each of the plurality of driving sources. It ispreferable that the desired displacement position adjacent theperipheral pressure points is horizontal.

In the press forming machine above, the control means may be providedwith means which measures a positional displacement adjacent each of thepressure points by the displacement measuring means on each of aplurality of operation stages during the press-forming operation,detects a state in which the vicinities of the peripheral pressurepoints are kept at a desired displacement position and a state in whichthe vicinity of the central pressure point is kept within apredetermined value from the desired displacement position, extracts acontrol data for each of the plurality of driving sources correspondingto the peripheral pressure points to keep the vicinities of theperipheral pressure points at the desired displacement position and acontrol data for the driving source corresponding to the centralpressure point to keep the vicinity of the central pressure point withina predetermined value from the desired displacement position, suppliesthe extracted control data to each of the plurality of driving sources,and individually drives each of the plurality of driving sources. It ispreferable that the desired displacement position adjacent theperipheral pressure points is horizontal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a press forming machine of an embodimentaccording to the present invention, which shows part of the pressforming machine by a cross section;

FIG. 2 is a top view of the press forming machine in FIG. 1, which showsthe press forming machine by removing part of an upper support plate;

FIG. 3 is a front view shown by enlarging an essential portion of FIG.1, which shows part of the essential portion by a cross section;

FIG. 4 shows a block diagram of a control system for the press formingmachine of the embodiment of the present invention, and

FIGS. 5A and 5B are graphs showing a relationship of a positional change(displacement) adjacent a pressure point on a pressure plates andforming time.

BEST MODE FOR CARRYING OUT THE INVENTION

First, a press forming machine of an embodiment according to the presentinvention is described below by referring to FIGS. 1, 2 and 3. The pressforming machine of the embodiment is a vertical press forming machine.FIG. 1 is a front view of the press forming machine of the embodimentaccording to the present invention, FIG. 2 is a top view of the pressforming machine, and FIG. 3 is a front view shown by enlarging part ofFIG. 1. FIG. 2 shows an upper support plate by removing part of thesupport plate. In the press forming machine, a fixed plate 10 is fixedon to the floor surface and the upper support plate 30 is held bysupports 20 set to the fixed plate. A pressure plate 40 capable ofreciprocating along the supports 20 is set between the fixed plate 10and the upper support plate 30 and there is a forming space between thepressure plate and the fixed plate. A fixed mold (bottom tool) 81 forpress is mounted on the fixed plate and a movable mold (top force) 82corresponding to the fixed mold is set to the downside of the pressureplate in the forming space so as to form a plate to be formed by settingthe plate between the both molds. The pressure plate 40 has slidingportions for sliding with four supports 20 at four corners of thepressure plate 40.

Five drives in which a servomotor is combined with a speed reducer aremounted on the upper support plate 30 as driving sources 60 a, 60 b, 60c, 60 d and 60 e. Driving shafts 61 a, 61 b, 61 c, 61 d and 61 eextending downward from the driving sources pass through through-holes71 a, 71 b, . . . , and 71 e formed on a reference plate 70 and engagewith engagement portions 62 a, 62 b, . . . , and 62 e at the upside ofthe pressure plate 40. Each engagement portion serves as a pressurepoint for transmitting a pressure to the pressure plate. A ball screw isset to each of the driving shafts so as to convert rotation intovertical movement and the pressure plate is vertically moved by rotationof the servomotors. The driving sources, the driving shafts and theengagement portions constitute the drives.

It is preferable that pressure points are arranged on the pressure plateso that pressures to the pressure plate by the driving shafts 61 a, 61b, 61 c, 61 d and 61 e are uniformly distributed on the pressure plate.At least one pressure point among three or more pressure points islocated between other pressure points or surrounded by other pressurepoints. It is preferable that every two pressure points among theplurality of pressure points are apart from each other with the samedistance. Moreover, it is preferable that these driving sources have thesame capacity of pressure, that is, the same output.

As shown by the top view in FIG. 2, the engagement portions 62 a, 62 b,62 c and 62 d are formed at the peripheral portion of the pressure plateclose to sliding portions between the pressure plate 40 and supports tosurround the forming region of the forming space. Thus, the engagementportions 62 a, 62 b, 62 c and 62 d serve as peripheral pressure points.The engagement portion 62 e surrounded by the four engagement portions62 a, 62 b, 62 c and 62 d is formed almost in the center of the pressureplate so as to press almost the center of the forming region. Therefore,the engagement portion 62 e serves as a central pressure point. The fourengagement portions 62 a, 62 b, 62 c and 62 d on the periphery are fixedto the pressure plate 40 and gaps or slack between the driving shaftsand the pressure plate are very small because the gaps are only producedby clearances between mechanical components. However, the engagementportion 62 e formed in the center preferably has a gap of 0.01 to 0.2 mmwhen there is no bending between the portion 62 e and the pressureplate. When press-formation is progressed, the reactive force to thepressure plate increases and the pressure plate 40 warps upward.Therefore, the force from the driving shaft 61 e may be applied to thepressure plate. FIG. 3 shows a partial view enlarging the engagementportion 62 e and the pressure plate 40. In the figure, two pins 65 arefixed on the upside of the pressure plate 40 and upper halves of thepins are protruded from the pressure plate. The pins 65 are insertedinto a hole 66 opened on a block of the engagement portion 62 e so thatthe block vertically moves relatively to the pins. When the drivingshaft 61 e does not press the pressure plate 40, there is a gap δ of0.01 to 0.2 mm between the bottom of the engagement portion 62 e and theupside of the pressure plate 40. If the pressure plate 40 is bent, thegap becomes small. When the pressure plate is further bent, the pressureplate 40 contacts the bottom of the engagement portion 62 e. Thus, thegap serves as the slack.

Moreover, displacement measuring means 50 a, 50 b, 50 c, 50 d and 50 eare mounted adjacent the respective engagement portions 62 a, 62 b, 62c, 62 d and 62 e. For each of the displacement measuring means 50 a, 50b, 50 c, 50 d and 50 e, it is possible to use means having a magneticscale provided with a magnetic graduation and a magnetic sensor such asa magnetic head facing the magnetic scale with a small gap. Byrelatively moving the magnetic sensor against the magnetic scale, theabsolute position and displacement speed of the magnetic sensor can bemeasured. Because the displacement measuring means is well known bythose skilled in the art, further description is omitted. Also,displacement measuring means for measuring a position by light or sonicwave may be used.

Magnetic scales 51 a, 51 b, . . . , and 51 e of the displacementmeasuring means 50 a, 50 b, 50 c, 50 d and 50 e are mounted on thereference plate 70 and magnetic sensors 52 a, 52 b, . . . , and 52 e ofthe displacement measuring means are supported by supports mounted onthe engagement portions 62 a, 62 b, 62 c, 62 d and 62 e. The referenceplate 70 is held at the same position independently from the position ofthe pressure plate 40. Therefore, when the pressure plate 40 is drivenby the driving sources 60 a, 60 b, 60 c, 60 d and 60 e, displacements ofthe engagement portions are measured by the displacement measuring means50 a, 50 b, 50 c, 50 d and 50 e.

The displacement measuring means 50 e mounted on the engagement portion62 e almost in the center of the pressure plate 40 does not measure adisplacement of the pressure plate but it measures a displacement of theengagement portion 62 e because a gap between the engagement portion 62e and the pressure plate is relatively large. It is possible to measurea displacement of the pressure plate 40 adjacent a pressure point on thepressure plate 40 by setting another displacement measuring means 50 e′mounted adjacent the engagement portion 62 e on the pressure plate 40 asshown by a double dotted line in FIG. 3. A difference between measuredvalues of the two displacement measuring means 50 e and 50 e′ becomesthe slack between the engagement portion 62 e and the pressure plateadjacent a pressure point of the engagement portion 62 e.

The reference plate 70 is set below the upper support plate 30 and fixedbetween the supports 20 and has through-holes 71 a, 71 b, . . . , and 71e respectively having a sufficiently-marginal diameter at a portionthrough which driving shafts 61 a, 61 b, . . . , and 61 e are passed sothat the reference plate is not influenced by deformations of thedriving shafts and the pressure plate. The upper support plate 30 andthe pressure plate 40 may be deformed as shown by a double dotted linein FIG. 1 depending on the shape of a workpiece in accordance with theprogress of press-formation. However, because the reference plate 70 isonly supported by the supports 20 at the corners, the reference platekeeps a reference position independently from deformations of thepressure plate and the upper support plate.

The reference plate 70 is supported by the supports 20 in thisembodiment. However, when it is necessary to avoid the influence ofelongations of the supports 20, it is possible to set another support toa lower support or fixed plate and support the reference plate.

FIG. 4 shows a control system diagram of the press forming machine.Before starting press-formation, a product name to be formed, formingpressures, and forming time are input from input means 91 to controlmeans 92 according to necessity in advance. The control means 92 has aCPU and driving pulse signals are sent from the control means 92 to thedriving sources 60 a, 60 b, 60 c, 60 d and 60 e through an interface 94to drive the driving sources for press-formation. Displacement signalsare sent to the control means 92 from the displacement measuring means50 a, 50 b, 50 c, 50 d and 50 e.

When press-formation is performed for a trial formation stage, forcesworking on the pressure plate are changed in accordance with progress ofthe press-formation. Loads to the driving sources 60 a, 60 b, 60 c, 60 dand 60 e are changed in accordance with the change of the forces. Apositional relationship between each portion of the movable moldcorresponding to each driving source and the fixed mold does not becomeuniform. At a driving source on which a large load works, the pressforming machine is deformed, particularly the pressure plate is bent,and the support is elongated. Moreover, in the case of an AC motor suchas a servomotor, delay in rotation of a rotor of the motor increases andthe lowering speed for lowering the pressure plate 40 is decreased.Lowering speed is relatively increased for other driving sources. Theadvance and delay are measured by the displacement measuring means 50 a,50 b, 50 c, 50 d, 50 e and 50 e′ and are sent to the control means 92 toadjust frequencies of driving pulse signals to the driving sources 60 a,60 b, 60 c, 60 d and 60 e so that displacements measured by thedisplacement measuring means 50 a, 50 b, 50 c, 50 d, 50 e and 50 e′become desired values, that is, parts of the pressure plate at theengagement portions become horizontal.

Thus, when forming a workpiece, control data including frequencies ofdriving pulse signals supplied to the driving sources is stored from thecontrol means into a memory on each of a plurality of operation stages.In this case, the plurality of operation stages include elapsed timesince the press-formation was started and lowering distance of thepressure plate or formation sequence since the press-formation wasstarted. For example, the time until the movable mold startspressurizing a plate to be formed after lowering the pressure plate orthe moving distance until pressurizing of the plate is started isassumed as a first operation stage. When the press-formation is startedafter that, minute elapsed time or lowering distance (minutedisplacement) is assumed as a operation stage of the press-formationbecause control data is greatly changed.

Then, control for the press-formation is described below. Driving pulsesignals are supplied to the driving sources and the pressure plate islowered to start press-formation. When the movable mold 82 comes to holdthe plate to be formed with the fixed mold 81, contacts with the mostprotruded portion of the mold, and starts forming the plate to beformed, the reactive force from the movable mold 82 is applied to thepressure plate. When assuming that frequencies of the driving pulsesignals supplied to the driving sources are constant, loads applied tothe driving sources do not become uniform when the reactive force fromthe plate to be formed starts applying to the pressure plate. Therefore,a driving source to which more load is applied receives largerresistance and the lowering displacement speed is decreased. However,the lowering displacement speed of a pressure point on the pressureplate corresponding to a driving source located at a portion with lessload is not changed or displacement may be relatively increased.Displacement measuring means close to each of the pressure points on thepressure plate measures the displacement, returns the measured value tothe control means 92, and the control means 92 adjusts the frequency ofthe driving pulse signal to be supplied to each driving source so as toreturn the pressure plate substantially to a horizontal state. Theadjusted driving pulse signal is stored in the memory 93 correspondinglyto each driving source in accordance with the displacement or time foreach operation stage.

FIGS. 5A and 5B show graphs in which positional displacement close to apressure point on the pressure plate is assigned to the axis of ordinateand forming time is assigned to the axis of abscissa. In FIGS. 5A and5B, FIG. 5A shows displacement close to an engagement portion 62 b as aperipheral pressure point and FIG. 5B shows displacement close to theengagement portion 62 e as a central pressure point. Moreover, the timeof start of the press-formation is assumed as S and the time of end ofthe press-formation is assumed as F. A dotted line connecting S and F isan arbitrary forming line (instruction value) (it is unnecessary thatthe dotted line is a straight line, but the dotted line may be anarbitrary curved line) and the forming line may be considered as aforming line corresponding approximately to an instruction value bywhich the entire pressure plate is lowering. FIG. 5A shows displacementvalues measured by the displacement measuring means 50 b by a thickline. Because the pressure plate horizontally lowers until a load isapplied, a straight line is formed between S and A. When application ofa large load starts at the point A, the driving sources receive a largeresistance, the pressure plate close to the pressure point to which theload is applied is deformed and time delay in displacement occurs, andthe distance from the fixed mold relatively increases compared to otherportions. Therefore, the displacement is delayed by ΔZAb from the idealforming line predicted for the pressure point for a certain elapsedtime. The displacement measuring means 50 b close to the pressure pointon the pressure plate measures the delay of the displacement, sends themeasured value to the control means 92, and the control means 92 makesthe frequency of the driving pulse signal to be supplied to the drivingsource 60 b higher than frequency to be sent to another driving sourceso as to make the pressure plate return to a desired displacement. Byrepeating the above adjustment, the displacement is made equal to adisplacement at other pressure points around the pressure plate at B.

When passing through B in FIG. 5A, the load applied to the drivingsource 60 b decreases. Therefore, the displacement is accelerated byΔZBb from the ideal forming line for a certain elapsed time. Therefore,the frequency of the driving pulse signal to be sent to the drivingsource 60 b is decreased by the control means 92 so as to make thepressure plate return to a desired displacement. By repeating thisadjustment, the operation reaches the press-formation end F. By applyingsimilar controls to other driving sources 60 a, 60 c and 60 d located onthe periphery of the pressure plate, it is possible to form the plate tobe formed, while keeping the entire pressure plate at desireddisplacement positions during the time of production press-formation. Asa result, it is possible to prevent angular moment from occurring on thepressure plate during the production press-formation.

Similarly to FIG. 5A, FIG. 5B shows a change of displacement around thecentral pressure point of the pressure plate with respect to time. Thedisplacement on the pressure plate closed to the central driving source60 e changes similarly to the displacement at the peripheral drivingsource 60 b before a load is applied. Because the engagement portion 62e has the gap δ, that is, the slack between the portion 62 e and thepressure plate, displacement of the engagement portion is present at aposition by the gap δ above the displacement of the pressure point shownby a thin solid line drawn from S to A in FIG. 5B. That is, thedisplacement is smaller by the gap δ. After point A, if the small loadcontinues to apply, the displacement of the engagement portionprogresses along a forming line predicted for the engagement portion, asshown by a thin dotted line obtained by extending the thin solid linedrawn from S to A beyond point A. The displacement of the engagementportion 62 e is measured by the displacement measuring means 50 emounted on the engagement portion 62 e that is movable relatively to thepressure plate.

In FIG. 5B, the displacement on the pressure plate is shown by a thicksolid line. The displacement on the pressure plate progresses from S′ toA′. After point A′, if the state in which the load is small iscontinued, the displacement progresses along a forming line predictedfor the pressure point on the pressure plate shown by a thick dottedline obtained by extending the straight thick solid line from S′ to A′beyond point A′. However, a larger load is applied after point A′. Theload may be larger than loads applied to pressure points on theperiphery. The displacement on the pressure plate is delayed from A′ dueto the load. When the delay of the displacement of the pressure plate orthe warped value at the central pressure point increases and the delayfrom the forming line predicted for the pressure plate exceeds δ, thepressure plate reaches the bottom of the engagement portion 62 e, andthe displacement intersects the thin solid line at point A. After that,the pressure by the driving source 60 e predominantly works, and thedisplacement progresses with a delay identical to the delay of theengagement portion 62 e, while the pressure plate is contacting to theengagement portion 62 e. A delay by ΔZAe for a certain elapsed timeoccurs from the forming line predicted for the engagement portion 62 e.To bring back the delay, the frequency of a driving pulse signal to besupplied to the driving source 60 e is raised. When the load decreasesand the delay or warped value of the central pressure point decreases,the displacement on the pressure plate adjacent the driving source 60 eis restored so as to maintain the above slack. The cycles are repeatedto perform the trial press-formation.

As described above, the delay ΔZAe of the engagement portion 62 e fromthe forming line predicted for the engagement portion 62 e is smallerthan the delay ΔZAe′ of the engagement portion 62 e from the idealforming line for the pressure points on the pressure plate by δ.

In the case of the graph depicted in FIG. 5A, a load of the engagementportion 62 b is kept small between B and C. In general, like the graphin FIG. 5B, the central engagement portion 62 e lowers so as to followother engagement portions 62 b, 62 c and 62 d on the periphery of thepressure plate while keeping the above δ in the gap. However, in somecases, as shown by the first period of C, even when the load of theengagement portion 62 b decreases as shown in FIG. 5A and a delay ΔZCbis small, a larger load is applied to the central engagement portion 62e, a delay ΔZCe larger than the above gap is caused, and the drivingsource 60 e may exhibit pressure.

In the first position where the bottom dead point F is reached, apressure is applied to a pressure point corresponding to the drivingsource 60 e and works so as to decrease the above gap to zero.

When the above-described gap δ is not present, it is necessary toperform control so as to create a pressure for compensating the delayΔZAe′ shown in FIG. 5B also in the central engagement portion 62 e andthe whole control may be locked or broken down because the drivingsource 60 e for supplying the pressure to the central engagement portion62 e is undesirably overloaded. However, when the gap δ is provided asdescribed above, it is enough to create a pressure for compensating thedelay ΔZAe shown in the graph and the probability in locking or brakingdown the whole control is greatly decreased.

In the above embodiment, it is described that the gap δ between theengagement portion 62 e and the pressure plate 40 is set to 0.01 to 0.2mm. When measuring the displacement of the pressure plate adjacent anengagement portion and performing control so as to keep the horizontalstate of the pressure plate, the portion at the central pressure pointis warped upward by the gap δ from portions at peripheral pressurepoints. Therefore, it is preferable to set the magnification of the gapδ to a value allowed as a bending value of the pressure plate. The gap δis set to the value because any trouble does not occur at each portionof a press forming machine with the gap value and because the warpcapable of sufficiently showing the accuracy of a workpiece normallyranges between 0.01 and 0.2 mm.

When there is not problem even if the warp of the pressure plateincreases at the portion of the central pressure point, it is alsopossible to perform control so that only peripheral pressure points arekept at desired displacement positions, for example, horizontally kept.

From a result of repeating the adjustment as described above, datacapable of executing production press-forming is obtained.

After the data capable of executing production press-forming is gatheredfor each of the plurality of driving sources, the obtained data (showingthe frequency of a driving source) is supplied to each of the drivingsources for the production press-forming. Moreover, each driving sourceindependently generates a pressure corresponding to the data. That is,driving is performed so as to progress from S to F as shown in FIGS. 5Aand 5B.

In other words, production press-forming is performed without performingfeedback control by checking a driving state among the driving sources.However, there is no temporal allowance for performing feedback controlin the production press-forming.

INDUSTRIAL APPLICABILITY

As described above in detail, the press forming machine of the presentinvention can avoid the overload of a central driving source to whichthe largest load is applied and keep a desired positional relationshipbetween a pressure plate (movable mold) and a fixed plate (fixed mold).

1. A press forming machine comprising: a fixed plate; a pressure platefacing the fixed plate, having a forming space between the pressureplate and the fixed plate and being capable of reciprocating; aplurality of driving shafts for pressing the pressure plate at three ormore respective pressure points distributed on the pressure plate byengaging with the pressure plate; a plurality of driving sources forrespectively driving the plurality of driving shafts; control means forindependently driving and controlling each of the plurality of drivingsources; and displacement measuring means for measuring a positionaldisplacement of the pressure plate adjacent each of the pressure points;wherein at least one pressure point (hereinafter referred to as “centralpressure point”) among the pressure points is set between or surroundedby other pressure points (hereinafter referred to as “peripheralpressure points”), a gap between a driving shaft engaged with thepressure plate at the central pressure point and the pressure plate islarger than a gap between a driving shaft engaged with each of theperipheral pressure points and the pressure plate, and the control meansis provided with means which measures the positional displacementadjacent each of the pressure points by the displacement measuring meanson each of a plurality of operation stages during a press-formingoperation, detects a state in which the entire pressure plate is kept atdesired displacement positions, extracts a control data for each of theplurality of driving sources to keep the entire pressure plate at thedesired displacement positions, supplies the extracted control data toeach of the plurality of driving sources, and individually drives theplurality of driving sources.
 2. A press forming machine as set forth inclaim 1, wherein the gap between the driving shaft engaged with thepressure plate at the central pressure point and the pressure plateranges between 0.01 and 0.2 mm.
 3. A press forming machine as set forthin claim 1, wherein the control means is provided with means whichmeasures a positional displacement adjacent each of the peripheralpressure points by the displacement measuring means on each of theplurality of operation stages during the press-forming operation,detects a state in which the vicinities of the peripheral pressurepoints of the pressure plate are kept at a desired displacementposition, extracts a control data for each of the plurality of drivingsources corresponding to the peripheral pressure points to keep thevicinities of the peripheral pressure points at the desired displacementposition, supplies the extracted control data to each of the pluralityof driving sources, and individually drives each of the plurality ofdriving sources.
 4. A press forming machine as set forth in claim 3,wherein the control means is provided with means which measures apositional displacement adjacent each of the peripheral pressure pointsby the displacement measuring means on each of the plurality ofoperation stages during the press-forming operation, detects a state inwhich the vicinities of the peripheral pressure points of the pressureplate are kept horizontal, extracts a control data for each of theplurality of driving sources corresponding to the peripheral pressurepoints, supplies the extracted control data to each of the plurality ofdriving sources, and individually drives each of the plurality ofdriving sources.
 5. A press forming machine as set forth in claim 1,wherein the control means is provided with means which measures apositional displacement adjacent each of the pressure points by thedisplacement measuring means on each of a plurality of operation stagesduring the press-forming operation, detects a state in which thevicinities of the peripheral pressure points are kept at a desireddisplacement position and a state in which the vicinity of the centralpressure point is kept within a predetermined value from the desireddisplacement position, extracts a control data for each of the pluralityof driving sources corresponding to the peripheral pressure points tokeep the vicinities of the peripheral pressure points at the desireddisplacement position and a control data for the driving sourcecorresponding to the central pressure point to keep the vicinity of thecentral pressure point within a predetermined value from the desireddisplacement position, supplies the extracted control data to each ofthe plurality of driving sources, and individually drives each of theplurality of driving sources.
 6. A press forming machine as set forth inclaim 5, wherein the control means is provided with means which measuresa positional displacement adjacent each of the pressure points by thedisplacement measuring means on each of the plurality of operationstages during the press-forming operation, detects a state in which thevicinities of the peripheral pressure points are kept horizontal and astate in which the vicinity of the central pressure point is kept withina predetermined value from a horizontal displacement position, extractsa control data for each of the plurality of driving sourcescorresponding to the peripheral pressure points to keep the vicinitiesof the peripheral pressure points horizontal and a control data for thedriving source corresponding to the central pressure point to keep thevicinity of the central pressure point within the predetermined valuefrom the horizontal displacement position, supplies the extractedcontrol data to each of the plurality of driving sources, andindividually drives each of the plurality of driving sources.
 7. A pressforming machine as set forth in claim 2, wherein the control means isprovided with means which measures a positional displacement adjacenteach of the peripheral pressure points by the displacement measuringmeans on each of the plurality of operation stages during thepress-forming operation, detects a state in which the vicinities of theperipheral pressure points of the pressure plate are kept at a desireddisplacement position, extracts a control data for each of the pluralityof driving sources corresponding to the peripheral pressure points tokeep the vicinities of the peripheral pressure points at the desireddisplacement position, supplies the extracted control data to each ofthe plurality of driving sources, and individually drives each of theplurality of driving sources.
 8. A press forming machine as set forth inclaim 2, wherein the control means is provided with means which measuresa positional displacement adjacent each of the pressure points by thedisplacement measuring means on each of a plurality of operation stagesduring the press-forming operation, detects a state in which thevicinities of the peripheral pressure points are kept at a desireddisplacement position and a state in which the vicinity of the centralpressure point is kept within a predetermined value from the desireddisplacement position, extracts a control data for each of the pluralityof driving sources corresponding to the peripheral pressure points tokeep the vicinities of the peripheral pressure points at the desireddisplacement position and a control data for the driving sourcecorresponding to the central pressure point to keep the vicinity of thecentral pressure point within a predetermined value from the desireddisplacement position, supplies the extracted control data to each ofthe plurality of driving sources, and individually drives each of theplurality of driving sources.